Air embolism produced in the brains of Mongolian gerbils served as an experimental model to correlate various parameters of the increased cerebrovascular permeability. 0.03-0.05 ml of air injected into the internal carotid artery resulted within a few minutes in a conspicuous breakdown of the BBB to the Evans blue albumin tracer. An increased permeability of protein tracers could also be shown by the application of horseradish peroxidase and it is demonstrable for approximately 5 hours. On the other hand, an abnormal passage of smaller molecule tracers such as sodium fluorescein and C14 sucrose was apparent even 24 hours following air embolism. Correlation of the BBB changes with cerebral blood flow (CBF) assessed by C14 antipyrine radioautography revealed an increased CBF in early stages and areas of greatly increased glucose phosphorylation to glucose-6-phosphate, without any spatial relationship to areas with abnormal BBB to various tracers.